This study is designed to determine the minimal effective oxytocin maintenance infusion required in labouring women undergoing cesarean delivery to achieve the best effect. Oxytocin is a drug that is routinely used to help the uterus to contract and keep it contracted after delivery. Consequently, it will help to reduce blood loss after delivery. In order to determine the minimal effective dose, the investigators will conduct a dose-finding study. The first patient will receive a set oxytocin infusion. The next patient's infusion dose of oxytocin, will either increase or decrease, depending on how the previous patient responds in terms of uterine tone. If the response is satisfactory with the infusion dose used, the next patient will either receive the same infusion dose or it will be decreased depending on a probability of 1:9. If the response is not satisfactory, then the infusion dose will increase for the next patient. The dose for each patient will be determined based on the results of the uterine contraction of the previous patient.
The investigators hypothesize that the ED90 of the oxytocin infusion rate to maintain adequate uterine tone in labouring women with induced or augmented labour undergoing cesarean delivery, following an initial effective bolus dose, would be lower than 0.74 IU/min (44 IU/h), which was found as the ED90 in a previous study, without an initial bolus dose prior to the infusion.
None
All patients who refuse to give written informed consent
All patients who declare allergy or hypersensitivity to oxytocin
A history of hypertension and/or severe cardiac disease(s)
All patients who have contraindications for neuraxial anesthesia
Parallel
Oxytocin
DrugOxytocin will be prepared in a 1L bag of Ringer's lactate, to be infused at a rate of 125 ml/h.
10
Treatment groupsSee each treatment group below.
Uterine tone up to discharge from the post anesthetic care unit (PACU): questionnaire
Uterine tone will be evaluated as satisfactory or unsatisfactory by the obstetrician throughout the surgery, starting at 5 minutes after the oxytocin infusion. It will also be measured at 10 minutes following the oxytocin infusion and every 10 minutes following that for the duration of the surgery. Unsatisfactory uterine tone at any time until discharge from the PACU will be considered a failure of the maintenance infusion.
Calculated blood loss
Estimated blood loss will be calculated using the difference in hematocrit values prior to surgery and 24 hours post surgery, using the following formula: Calculated blood loss (mL) = EBV ((Pre-op Htc-Post-op Htc)/pre-op Htc) EBV (estimated blood volume) in ml: patient's weight in kg x 85.
Need for blood transfusion
Blood product administered.
Episodes of bleeding postpartum
Number of episodes of bleeding postpartum up to 24 hours post delivery.
Intraoperative requirement for additional uterotonic medication
A request made by the obstetrician performing the cesarean delivery for additional uterotonic medication, due to bleeding or poor uterine tone.
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